Primary large-cell lymphomas of the mediastinum.

The mediastinum is a frequent site of involvement for malignant lymphoma. The most common types encountered in this location include Hodgkin's and non-Hodgkin's lymphoma and lymphoblastic lymphoma. With the exception of lymphoblastic lymphoma in children and adolescents, most cases of mediastinal involvement by lymphoma represent part of systemic disease and do not generally pose difficulties for diagnosis. However, a relatively small group of tumors have become increasingly recognized in recent years that are primarily localized in the anterior mediastinum and show features of nonlymphoblastic/non-Hodgkin's large-cell lymphoma. Because such tumors are capable of adopting unusual morphological appearances, they can often pose difficulties for diagnosis and be frequently mistaken for other conditions. This review discusses this group of neoplasms collectively known as diffuse large-cell lymphoma of the mediastinum. The clinicopathologic, immunohistochemical, and molecular genetic aspects of these tumors appear to indicate that a significant proportion of them may correspond to a distinctive type of lymphoproliferative process most likely arising from a native B-cell population of the thymus, thus representing, in essence, a primary extranodal large-B-cell lymphoma of the thymus.